1. Field of the Invention
The present invention generally relates to a tamper-resistant security system for and method of controlling the operation of an access device and, more particularly, to a tamper-resistant electronically controlled garage door opener system and method of operating and installing the same.
2. Description of the Prior Art
Electronically controlled garage doors are typically opened or closed by radio signal commands coming from a remote control wireless transmitter located inside an automobile which an operator wishes to park in the garage, or from an interior push-button switch located at a convenient location inside the garage, or from an exterior key-operated switch located on the garage door jamb outside the garage. Due to the inconvenience for an operator to carry the key on his person, exterior keyless electronic locks, such as described in U.S. Pat. No. 3,978,376, have been proposed.
The known exterior key-operated switches and keyless electronic locks both operate by momentarily closing two electrical conductors or control wires which extend from the exterior key-operated switch or keyless lock, through the door jamb, and into the interior of the garage for connection to a conventional control-processor unit which, in turn, is connected to a motor drive and which, in turn, is connected to the electro-mechanical garage door opener mechanism itself. The momentary closing of the two control wires creates a short circuit condition which activates the opener mechanism to open the garage door.
However, the known exterior key-operated switches and keyless electronic locks are easily tampered with by an intruder who wishes to gain entry into the garage, but who has no key or does not know the lock combination. For example, both the key-operated switches and keyless locks can each be easily physically pulled from the garage door jamb, and thereupon, the intruder can easily short the two exposed control wires to open the garage door. As for the key-operated switches, they can also be overcome by merely picking the lock cylinder.
The aforementioned U.S. Pat. No. 3,978,376 is typical of those keyless electronic locks wherein the keyboard and the control-processor unit are both located exteriorly of the garage on the door jamb. As noted above, a serious shortcoming of this type of system is its susceptibility to physical force which would expose the two control wires. An intruder can easily pull the keyboard with its attached control-processor unit off the door jamb, and thereupon, short the exposed wires to activate the opener mechanism.
In order to overcome this lack of security, it has been proposed, e.g. in U.S. Pat. No. 3,633,167, to separate the keyboard from the control-processor unit. In this approach, the keyboard is mounted on the door jamb, and the control-processor unit is mounted behind the garage door within the interior garage area. However, this approach requires running approximately N+1 wires (where N equals the number of switches on the keyboard) from the keyboard located outside the door to the control-processor unit located inside the garage. In typical applications where there are ten switches on the keyboard, this would mean that approximately eleven wires must be separately connected to the keyboard, and thereupon, separately connected to the control-processor unit. Also, all of the eleven wires must be routed through a mounting hole formed in the door jamb. In sum, this multi-wire technique is both expensive and complicated to install. Retrofitting to an existing installation is also much more difficult.